In the conventional arrangement, electrostatic handling devices for wafers comprise a layer of dielectric material for carrying a wafer to be processed and conductor lines or wires which pass through the dielectric material. When a voltage is applied to the conductor lines, an electrostatic force (i.e. an electric field creating a coulombic force) is produced which polarizes, at least temporarily, both the wafer and the dielectric material. This causes the wafer and dielectric material to be attracted to one another by electrostatic force. Prior art electrostatic handling devices typically employ two groups of interdigitated conductors having uniform spacing between adjacent conductors, with the groups of interdigitated conductors being connected between one or more voltage sources. The interdigitated conductors may be formed as interdigitated straight parallel lines, as illustrated in U.S. Pat. No. 4,184,188 to Briglia, or as interdigitated concentric rings, as illustrated in U.S. Pat. No. 4,724,510 to Wicker, et al. Other arrangements may also be employed.
Unfortunately, the electric field generated with the prior art electrostatic handling devices is quite large (e.g. greater than 5kV) and extends into the region at or above the wafer face to be processed. This electric field may degrade a number of wafer processing operations and simply cannot be tolerated in other operations. For example, reactive ion etching, plasma etching, sputtering, and ion implantation cannot properly take place in the presence of such a large strength electric field near the wafer. For these operations, the prior art often had to employ mechanical or vacuum handling devices which are complicated and introduce a new set of problems.
One attempt to reduce the electric field generated with the prior art electrostatic handling devices has employed a polarizable dielectric for the layer of dielectric material. The polarizable dielectric material retains charge even after the voltage is received from the conductive lines, so that the voltage on the conductive lines need not be maintained. Unfortunately, the use of a polarizable dielectric material makes it difficult to remove the wafer from the handling device after processing is complete because the retained charge in the dielectric material continues to attract the wafer. The fragile wafers often break during removal, or portions of the dielectric material separate from the electrostatic handling device, thereby rendering the wafer and device unusable.